This invention relates to opto-electronic devices and, in particular, to optical amplifiers obtained by coating the facets of a laser with anti-reflection coating.
Semiconductor lasers are well known devices which are used to generate light. Their operation depends upon the reflection of light generated by the device back into the device. It is also desired to utilise a "laser" to amplify a received optical signal. In this application it is desired that the device shall respond only to the received signal and in order to achieve or get close to this result it is necessary to eliminate as far as it is possible the reflection of light back into the device.
For this purpose, anti-reflection coatings are applied to the facets of the laser and a wide variety of metal oxides have been proposed for these coatings, e.g. Al.sub.2 O.sub.3, Sc.sub.2 O.sub.3, ZrO.sub.2 and CeO.sub.2. Our copending U.S. application Ser. No. 741,867 filed June 6, 1985 derived from UK patent application No. 8414454 state that oxides of Y, Gd, Nd and La give particularly good results.